#include<stdio.h>

const double pi = 3.141592653;

int main()
{
    double r = 0;
    double s = 0;
    printf("请输入半径：\n");
    scanf("%lf",&r);

    s = pi * r * r;
    printf("圆的面积：%lf\n",s);

    return 0;
}